The present invention relates to a method for operating a telecommunications system containing a plurality of local exchanges in which signaling and traffic data are routed via a network service having routing code recalculation. The method is adapted to provide an integrated services digital network (ISDN) end-to-end supplementary service involving an interaction between two subscribers connected to a local exchange in which knowledge of the subscriber access code used in a called subscriber local exchange is required in the calling subscriber local exchange. The subscriber access code is generated by modification of a called subscriber routing code used by a calling subscriber local exchange. The modification occurs in a transit exchange or a service control point having a translation capability for converting the called subscriber routing code into the subscriber access code. Each local exchange has an application service element for providing the ISDN end-to-end supplementary service.
ISDN end-to-end supplementary services using end-to-end signaling, as defined in ITU-T Recs., e.g. I.253.3, do not work if number translation is required.
A completion of calls to busy subscriber (CCBS) supplementary service is one example of a subscriber service which uses end-to-end signaling, and in which the service is implemented by operations performed in both a calling subscriber local exchange and a called subscriber local exchange. Implementation of a CCBS service requires that the calling subscriber local exchange has knowledge of the called subscriber access code, as used in the called subscriber local exchange.
Completion of calls to a busy subscriber is defined in ITU-T Recommendation I.253.3.
The completion of calls to busy subscribers (CCBSs) supplementary service enables a calling user A, upon encountering a busy destination B, to be notified when the busy destination B becomes free and to have the service provider reinitiate the call to the specified destination B if user A desires. The CCBS supplementary service is applicable to users who are connected to the network via a basic access or a primary rate access. The CCBS supplementary service enables user A, upon encountering a busy destination B, to have the call completed without having to make a new call attempt when destination B becomes free. When user A requests the CCBS supplementary service, the network will monitor for destination B becoming free. When destination B becomes free, then the network will wait a short time as defined in the destination B idle guard timer in order to allow the resources to be reused for originating a call. If the resources are not reused by destination B within this time, then the network will automatically recall user A. When user A accepts the CCBS recall, then the network will automatically generate a CCBS call to destination B.
Global virtual network service (GVNS) is one example of a network service that modifies the routing code (dialed number), with the result that there is no transparency through the network for the called subscriber access code, as used in the called subscriber local exchange.
The global virtual network service is defined in ITU-T Recommendation F.16. The global virtual network service (GVNS) is a multi-network international service that provides private network functions to users at geographically dispersed international locations while minimizing the need for dedicated network resources. It may be offered to customers over the PSTN and/or ISDN. The global virtual network service is a feature-rich communications service. It provides the functions typically associated with the private networks, but utilizing the public switched network(s). The GVNS customer network configuration is defined per customer direction using customer-specific service information resident in multiple networks. The network configurations may be administered by the GVNS customer directly, the GVNS participating service provider(s) and/or the GVNS co-ordinator(s). The GVNS provides the customers with global services as a result of internetworking among the GVNS participating service providers in various countries. GVNS may accommodate this interconnection both via ISDN and non-ISDN facilities.
International Patent Disclosure WO 97/17794 describes a solution to provide CCBS over GVNS for a telecommunications system containing a plurality of local exchanges in which signaling and traffic data are routed between local exchanges via a network service having routing code recalculation. The network service includes a plurality of transit nodes, and a method to provide a supplementary subscriber service involving an interaction between two subscribers. In the method knowledge of a subscriber access code, used in a called subscriber local exchange, is required in a calling subscriber local exchange. The subscriber access code is generated by modification of a called subscriber routing code, used by the calling subscriber local exchange; and the modification occurs in a transit node of the network service.
According to International Patent Disclosure WO 97/17794 the telecommunications system is characterized in that at least some GVNS transit nodes include a relay applications service element (see International Patent Disclosure WO 97/17794, FIG. 3, new completion of calls to busy subscriber application service element (CCBS-ASE)) which is adapted to relay signaling data between local exchanges and which includes translation capabilities for converting a subscriber access code used at a called subscriber local exchange into a called subscriber routing code used by a calling subscriber exchange, and in that signaling data is transmitted between the calling and the called local exchanges via the relay application service element CCBS-ASE in the GVNS transit node.
For the backward direction (local exchange of the called subscriber to local exchange of the calling subscriber) the subscriber access code has to be translated into the called subscriber routing code and signaling data has to be transmitted between the called and the calling local exchanges via the relay application service element CCBS-ASE in the GVNS transit node.
In addition to the requirement of the relay application service element CCBS-ASE in the GVNS transit node the solution requires resources such as transaction IDs (transaction identifiers, see Table 1, positions 24, 25 below). In the GVNS transit node, where two sections of an the end-to-end dialog are connected, all messages being part of the dialog have to pass through the complete protocol stack (up and down) which increases the propagation delay of the messages.
It is accordingly an object of the invention to provide a telecommunications system and a method relating to telecommunications services with number translation which overcome the above-mentioned disadvantages of the prior art devices and methods of this general type.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for operating a telecommunications system containing a plurality of local exchanges in which signaling and traffic data are routed via a network service having routing code recalculation. The method is adapted to provide an integrated services digital network (ISDN) end-to-end supplementary service involving an interaction between two subscribers each connected to a local exchange in which knowledge of a subscriber access code used in a called subscriber local exchange is required in a calling subscriber local exchange. The subscriber access code is generated by modification of a called subscriber routing code used by the calling subscriber local exchange. The modification occurs in a transit exchange or a service control point each having a translation device for converting the called subscriber routing code into the subscriber access code. Each of the local exchanges is connected to an application service element for providing the ISDN end-to-end supplementary service. The method includes providing the local exchanges supporting the ISDN end-to-end supplementary service with a trigger mechanism for triggering and forwarding a query to the translation device whenever the ISDN end-to-end supplementary service is requested and when the called subscriber routing code is detected. The subscriber access code thus returned from the translation device is forwarded to the application service element, which, based on a received subscriber access code, will establish one and only one end-to-end dialogue with an associated counterpart at the called subscriber local exchange and provide the ISDN end-to-end supplementary service.
The method in accordance with the invention allows a direct, unchained dialogue between the application service element 1 by introducing a trigger mechanism. In a preferred embodiment the trigger mechanism is located in the call control function of the local exchange of the calling subscriber. In a further step the trigger mechanism is equipped with a memory unit, which at least temporarily retains the translated number. The invention also has application to interacting between any network service with routing code (dialed number) recalculation, referred to as number translation and any ISDN end-to-end supplementary service.
With GVNS, as initially defined, there is nothing to prevent a terminating local exchange sending a CCBS possible indicator in the backward release message, since that exchange cannot distinguish between a normal call and a GVNS call. Thus, the CCBS possible indicator is repeated all the way back to the originating exchange. If no solution is found to the problem, all GVNS calls, for which completion of calls to busy subscriber (CCBS) is requested, will lead to unnecessary signaling procedures. The problem created by the interaction between the CCBS and the GVNS will not be solved by simply omitting CCBS for GVNS calls. The CCBS request must either be prevented, or some method for handling it must be provided.
The present invention is based on a telecommunications system containing a plurality of local exchanges in which signaling and traffic data are routed between local (remote) exchanges via a network service having routing code (dialed number) recalculation, referred to as number translation, which network includes a plurality of transit nodes and/or nodes of the intelligent network. The telecommunications system being adapted to provide an ISDN end-to-end supplementary service involving an interaction between two subscribers requires:
knowledge of a subscriber access code, used in a called subscriber local exchange, is required in a calling subscriber local exchange;
the subscriber access code is generated by modification (number translation) of a called subscriber routing code (dialed number), used by the calling subscriber local exchange; and
the modification (number translation) occurs in a transit node or in a service control point of the network service.
According to a first aspect of the present invention the telecommunications system is characterized in:
that a call control function in each local exchange contains a trigger mechanism for providing access to a number translation function to allow for the supplementary service,
that at least some transit nodes or service control points include an application for converting a subscriber routing code (dialed number) used by a calling subscriber local exchange into a called subscriber access code used at a called subscriber local exchange,
that the converted number is sent back to the calling subscriber local exchange, and
that in the calling subscriber local exchange the subscriber routing code (dialed number) is linked to the called subscriber access code.
Preferably the ISDN end-to-end supplementary service is a CCBS service. Preferably the network service having routing code (dialed number) recalculation (number translation) is a GVNS service. Preferably the telecommunications system is a single unitary ISDN system. A CCBS-ASE may be located in each local exchange within the telecommunications system providing CCBS to subscribers connected thereto. Each of the plurality of transit nodes or service control points may be adapted, in use, to receive a request for number translation from a local exchange, providing CCBS to subscribers connected thereto, has an application for number translation located therein. Preferably the application is restricted to the number translation function.
In accordance with an added mode of the invention, there is the step of basing the translation device on a global virtual network service (GVNS) function located in a transit exchange or in a service control point and during the forwarding step the subscriber access code depending from the called subscriber routing code is taken from a database.
In accordance with an additional mode of the invention, there are the steps of locating the trigger mechanism in a call control function of the calling subscriber local exchange; and storing the called subscriber routing code in a memory location of the call control function assigned to the local exchange from which a call was originated is replaced by the subscriber access code and stored in the memory location.
In accordance with a further mode of the invention, there is the step of providing the translation device in the service control point and there is a service switching function contained in the local exchange and during the forwarding step the local exchange acts temporarily as the service switching point.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a telecommunications system and a method relating to telecommunications services with number translation, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.